1. Field of the Invention
This invention relates to an optical wavelength converting apparatus for converting a fundamental wave into its second harmonic, or the like. This invention particularly relates to an optical wavelength converting apparatus, wherein a semiconductor laser and an optical wavelength converting device are combined with each other.
2. Description of the Prior Art
Various attempts have heretofore been made to convert the fundamental wave of a laser beam into its second harmonic, or the like, e.g. to shorten the wavelength of a laser beam, by using a nonlinear optical material. As optical wavelength converting devices for carrying out such wavelength conversion, there have heretofore been known a bulk crystal type of optical wavelength converting device, an optical waveguide type of optical wavelength converting device, and the like. These types of optical wavelength converting devices are often combined with semiconductor lasers.
In order to obtain a high efficiency, with which the wavelength conversion is effected, when a semiconductor laser and an optical wavelength converting device are combined with each other, it has been proposed to incorporate the optical wavelength converting device in the region inside of a resonator of the semiconductor laser. Such optical wavelength converting apparatuses are disclosed in, for example, Japanese Unexamined Patent Publication Nos. 62(1987)-86881 and 3(1991)-3287. With the disclosed optical wavelength converting apparatuses, a rear end face of the semiconductor laser and a front end face of the optical wavelength converting device are utilized as mirror surfaces of the resonator of the semiconductor laser. In this manner, the intensity of a fundamental wave, which passes through the optical wavelength converting device, is increased, and a high wavelength conversion efficiency can be obtained.
However, the wavelength of the fundamental wave, which is produced by the oscillation of the semiconductor laser, fluctuates in accordance with the level of a drive current fed to the semiconductor laser and the temperature of the semiconductor laser. Therefore, in the aforesaid optical wavelength converting apparatuses, the wavelength of the fundamental wave, which is produced by the oscillation of the semiconductor laser, fluctuates easily. If the wavelength of the fundamental wave fluctuates and goes beyond a range of wavelengths, at which the phase matching between the fundamental wave and its second harmonic, or the like, can be effected, the wavelength conversion efficiency inevitably becomes low.